Unformatted text preview: In dim light, the opposite happens; the pupil
expands to allow more light into the eye.
(b) Control of over the entry of light is appropriate
as a reflex activity because the response is
immediate and unconscious. In this way, the eye
can be protected against damage and vision Biozone International 2009 Photocopying Prohibited 15
8. Each type of cone, blue, green and yellow-green (or
red), responds maximally to one particular wavelength
of light. The differential response of the cones to light
is interpreted by the brain as color. metabolism.
Examples: insulin and glucagon, parathormone
(increases blood calcium) and calcitonin (lowers
(b) In general principle, the product of a series of
(hormone controlled) reactions controls its own
production by turning off the pathway when it
reaches a certain level. If there is too little of the
product, its production is switched on again. Hearing (page 89)
1. 2. (a) Ear drum: Vibrates in response to sound waves.
(b) Ear ossicles: Transmit the sound waves from the
ear drum to the smaller oval window.
(c) Oval window: Amplifies the sound waves before
they enter the fluid filled inner ear (because of its
smaller surface area).
(d) Sensory hair cells: Respond to the stimulus
of pressure waves in the fluid filled inner ear by
generating electrical impulses.
(e) Auditory nerve: Transmits the impulses from the
sensory hair cells to the brain for processing. 2. Only the target cells have the appropriate receptors
on the membrane to respond to the hormone. Other
(nontarget) cells will not be affected. 3. (a) Hormones must circulate in the blood to reach
the target cells and a metabolic response must be
initiated. This takes some time.
(b) Hormones bring about a metabolic change and
often start a sequence of cascading, interrelated
events. Once started, these events take time to
conclude. Nervous responses continue only for
the time that the stimulation continues. Sound waves are converted into pressure waves
in the fluid. Because fluid is...
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This document was uploaded on 01/28/2014.
- Winter '13